6 Predictions of new stellar $\mathsf{H_{2}}$O masers

Figure 9: The physical conditions giving rise to bright emission at the epoch of our calculations. a) Radial distribution of maser emission; b) gas velocity as a function of radial distance; c) $T_{\rm k}$; d) n(H2). Marked on the plots are the radial extents of the brightest 10$\%$ of components produced by the model at 325, 183, 321 and 22GHz.

Some transitions which produce strong maser emission in the model have never been detected towards stellar environments. Many have been predicted by other models, for example those of Neufeld & Melnick (1991) and Y97. However, these models did not predict the line profiles and images expected for new masers. Some examples of predicted maser lineshapes are shown in Fig. 10. The lines are considered to be of an observable strength as they have intensities comparable to, and sometimes higher than, the 22, 321 and 325GHz masers at the same epoch, see Fig. 3. The transitions which must be inverted to produce the new masers are listed in Table 6. Noting that many H₂O lines are obscured by atmospheric attenuation, we provide an indication of those masers which may be observable by satellite missions such as the Herschel Space Observatory (HSO). We discuss the spatial structure of such masers in Sect. 7.

   

Table 6: The stellar H₂O masers predicted by our simulations.

Frequency	Transition	$E_{\rm u}$	Observable by
(GHz)		(K)	the HSO?
*380	4 $_{14} \rightarrow 3_{21}$	324	N
448	4 $_{23} \rightarrow 3_{30}$	433	N
970	5 $_{24} \rightarrow 4_{31}$	599	Y
1322	$6_{25} \rightarrow 5_{32}$	796	N
1158	6 $_{34} \rightarrow 5_{41}$	935	Y
1542	6 $_{33} \rightarrow 5_{42}$	953	Y
1441	7 $_{26} \rightarrow 6_{33}$	1022	Y
1766	7 $_{35} \rightarrow 6_{42}$	1176	Y
1296	$8_{27} \rightarrow 7_{34}$	1275	N
2245	$8_{36} \rightarrow 7_{43}$	1449	N
906	9 $_{28} \rightarrow 8_{35}$	1556	Y
2532	9 $_{37} \rightarrow 8_{44}$	1751	N
2575	10 $_{38}\rightarrow 9_{45}$	2082	N

^* Already observed towards a star-forming region.

Figure 10: Some maser lineshapes predicted by the model at 1296, 970 and 448GHz. The lineshape intensity is normalised to the peak intensity of the 22GHz maser lineshape in Fig. 3.